fix: audioSession playback type, exponential backoff, pageshow recovery

- Set navigator.audioSession.type = 'playback' on first play — tells Android
  OS this is a music app, keeping background network alive through Doze mode
- Replace flat 2s error retry with exponential backoff (1s/2s/4s/8s)
- Add pageshow event alongside visibilitychange for Samsung/iOS PWA reliability
- Attempt audio resume on foreground if OS killed playback while backgrounded
- Switch preload from hidden audio element to link rel=prefetch (lighter,
  avoids triggering two-audio-stream detection on Android)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/main.js

@@ -127,6 +127,8 @@ window.addEventListener('load', () => {
   S.audio.addEventListener('ended', onEnded);
   S.audio.addEventListener('play', () => {
     S._trackChanging = false;
+    // Tell OS this is a music playback app — keeps background network alive (Doze mode)
+    try { if(navigator.audioSession) navigator.audioSession.type = 'playback'; } catch {}
     absInterrupt();
     setPlayIcon(true);
     document.getElementById('player-art').classList.add('spinning');
@@ -143,24 +145,34 @@ window.addEventListener('load', () => {
 
   // stalled = browser buffer ran out briefly; let the browser retry naturally.
   // The watchdog below catches genuine long freezes.
+  let _errRetries = 0, _errTimer = null;
+  S.audio.addEventListener('play', () => { _errRetries = 0; clearTimeout(_errTimer); }, { capture: true });
   S.audio.addEventListener('error', () => {
-    if(S.queue[S.qIdx]) {
+    if(!S.queue[S.qIdx]) return;
-      const t = setTimeout(() => { S.audio.load(); S.audio.play().catch(()=>{}); }, 2000);
+    _errRetries++;
-      S.audio.addEventListener('play', () => clearTimeout(t), { once: true });
+    const delay = Math.min(1000 * Math.pow(2, _errRetries - 1), 8000); // 1s, 2s, 4s, 8s
-    }
+    clearTimeout(_errTimer);
+    _errTimer = setTimeout(() => { S.audio.load(); S.audio.play().catch(() => {}); }, delay);
   });
 
   S.audio.volume = 0.5;
 
-  // Re-register MediaSession handlers when returning from background/screen-off/flip
+  function _onForeground() {
-  document.addEventListener('visibilitychange', () => {
-    if(document.visibilityState !== 'visible') return;
     const s = S.queue[S.qIdx];
     if(!s) return;
     updateMediaSession(s);
     if(navigator.mediaSession)
       navigator.mediaSession.playbackState = S.audio.paused ? 'paused' : 'playing';
+    // If audio was playing before backgrounding but is now paused (OS kill), try to resume
+    if(!S.audio.paused) return;
+    if(s && S.audio.src) S.audio.play().catch(() => {});
+  }
+
+  document.addEventListener('visibilitychange', () => {
+    if(document.visibilityState === 'visible') _onForeground();
   });
+  // pageshow fires more reliably than visibilitychange on iOS PWA and Samsung
+  window.addEventListener('pageshow', e => { if(e.persisted) _onForeground(); });
 
   // Watchdog: detect when audio silently stalled in background (ended event not fired, or frozen)
   let _wdLast = 0, _wdStalledAt = 0;

src/player.js

@@ -5,10 +5,10 @@ import { api, streamUrl, coverUrl, downloadUrl } from './api.js';
 import { loadRecommendations } from './views.js';
 import { updateLyricsHighlight, onNpSongChange } from './nowplaying.js';
 
-// ─── PRELOAD (keeps network alive through Doze mode gap between tracks) ───
+// ─── PRELOAD (resource hint keeps connection open through Doze gap) ───
-let _preAudio = null;
 let _preUrl  = '';
 let _preId   = '';
+let _preLink = null;
 
 function _nextIdx() {
   if(S.repeat === 'one') return S.qIdx;
@@ -25,14 +25,17 @@ function _preloadNext() {
   if(!next || _preId === next.id) return;
   _preId  = next.id;
   _preUrl = streamUrl(next.id);   // generate URL once — reused by main element
-  if(!_preAudio) { _preAudio = new Audio(); _preAudio.preload = 'auto'; }
+  if(_preLink) _preLink.remove();
-  _preAudio.volume = 0;
+  _preLink = document.createElement('link');
-  _preAudio.src = _preUrl;        // Chrome starts buffering immediately
+  _preLink.rel  = 'prefetch';
+  _preLink.as   = 'fetch';
+  _preLink.href = _preUrl;
+  document.head.appendChild(_preLink);
 }
 
 function _clearPreload() {
   _preId = ''; _preUrl = '';
-  if(_preAudio) { _preAudio.src = ''; }
+  if(_preLink) { _preLink.remove(); _preLink = null; }
 }
 
 // ─── PLAYBACK ───